This invention relates to a process to prepare monomers, more specifically this invention relates to a transesterification process to prepare (meth)acrylate monomers.
It is known, for example in EP-A-0,902,017, that (meth)acrylates of Formula I, such as N-(2- methacryloyloxyethyl) ethylene urea (MEEU), and the alcohol of Formula IV, such as methanol, may be produced by the transesterification of an alkyl (meth)acrylate of Formula II, such as methyl methacrylate (MA) with a hydroxyl alkyl imidazolidin-2-one of Formula III, such as hydroxyethyl ethylene urea (HEEU), using a transesterification catalyst and in the presence of a polymerization inhibitor. 
where R=H or CH3;
where Rxe2x80x3=C1-C8 straight or branched alkylene; 
where R=H or CH3; and
where Rxe2x80x2=C1-C8 straight or branched alkyl; 
where Rxe2x80x3=C1-C8 straight or branched alkylene;
Rxe2x80x2xe2x80x94OHxe2x80x83xe2x80x83FORMULA IV
where Rxe2x80x2=C1-C8 straight or branched alkyl.
Conventionally, the transesterification catalyst is added to the well-mixed reaction mixture containing the alkyl (meth)acrylate of Formula II and the hydroxyl alkyl imidazolidin-2-one of Formula III. We have unexpectedly discovered that level of conversion of the hydroxyl alkyl imidazolidin-2-one of Formula III to the (meth)acrylate of Formula I may be increased for the above-described transesterification process by ensuring that the transesterification catalyst has ample opportunity to be in contact with the hydroxyl alkyl imidazolidin-2-one of Formula III by introducing the transesterification catalyst to the hydroxyl alkyl imidazolidin-2-one of Formula III while the reaction mixture is unagitated.
We have discovered an improved process for forming the (meth)acrylate monomer of Formula I: 
where R=H or CH3;
where Rxe2x80x3=C1-C8 straight or branched alkylene; comprising the sequential steps of:
(1) forming a reaction mixture, comprising:
(a) hydroxyl alkyl imidazolidin-2-one of Formula III: 
xe2x80x83where Rxe2x80x3=C1-C8 straight or branched alkylene;
(b) 10 to 10,000 ppm, based on weight of said hydroxyl alkyl imidazolidin-2-one of Formula III, of at least one polymerization inhibitor selected from the group consisting of diethylhydroxylamine, p-methoxy phenol, hydroquinone, phenothiazine, 4-hydroxy-2,2,6,6-tetramethyl piperidnyl free radical, 4-methacryloyloxy-2,6,6-tetramethyl piperidinyl free radical, and 4-hydroxy-2,6,6-tetramethyl N-hydroxy piperidine;
(2) adding to said reaction mixture 0.1 to 10 mole % of a transesterification catalyst selected from the group consisting of dibutyl tin oxide, reaction products of dibutyl tin oxide with components in the transesterification of various alcohols with alkyl (meth)acrylates; dibutyl tin dimethoxide, reaction products of dibutyl tin dimethoxide with components in the transesterification of various alcohols with alkyl (meth)acrylates; methanolic magnesium methylate; lithium; lithium carbonate; anhydrous alkali metal hydroxide; hydrates of alkali metal hydroxide; and mixtures thereof;
wherein said reaction mixture is unagitated when said catalyst is added;
(3) adding to said reaction mixture at least one alkyl (meth)acrylate of Formula II: 
where R=H or CH3; and
where Rxe2x80x2=C1-C8 straight or branched alkyl; under conditions to effect the transesterification of said alkyl (meth)acrylate of Formula II and said hydroxyl alkyl imidazolidin-2-one of Formula III to form a (meth)acrylate of Formula I: 
where R=H or CH3;
where Rxe2x80x3=C1-C8 straight or branched alkylene; and the alcohol of Formula IV:
Rxe2x80x2xe2x80x94OHxe2x80x83xe2x80x83FORMULA IV
where Rxe2x80x2=C1-C8 straight or branched alkyl; and
wherein the mole ratio of said hydroxyl alkyl imidazolidin-2-one of Formula III to total said alkyl (meth)acrylate is from 1:1 to 1:20.
The reaction mixture may further comprise an alkyl (meth)acrylate of Formula II: 
where R=H or CH3; and
where Rxe2x80x2=C1-C8 straight or branched alkyl.
The process may further comprise the step of azeotropically removing a mixture of said alkyl (meth)acrylate of Formula II and said alcohol of Formula IV.
The process may further comprise the step of adding water to enable recycling of said transesterification catalyst, if said catalyst has low water solubility.
The process may further comprise the step of recycling the alkyl (meth)acrylate of Formula II.
The process may further comprise the step of distilling the (meth)acrylate of Formula I.
It is not necessary to separate the catalyst or catalyst by-products from the reaction mixture. In addition, it is not necessary to separate the catalyst or catalyst by-products from the reaction mixture, under process conditions where:
(a) excess alkyl (meth)acrylate is used and diluted with water; or
(b) the reaction mixture is treated with water to effect an exchange of the excess alkyl (meth)acrylate with water to produce a mixture of (meth)acrylate of Formula I in water.
There are a number of different ways that the transesterification catalyst may be exposed to increased contact with the hydroxyl alkylene imidazolidin-2-one of Formula III relative to conventional processes. This includes introducing the transesterification catalyst to the hydroxyl alkylene imidazolidin-2-one of Formula III while the reaction mixture is unagitated and wherein the reaction mixture includes:
(a) the hydroxyl alkylene imidazolidin-2-one of Formula III neat (i.e., molten and not provided in solvent, including monomers such as alkyl (meth)acrylate of Formula II); or
(b) the hydroxyl alkylene imidazolidin-2-one of Formula III combined with the alkyl (meth)acrylate of Formula II.
The process of this invention is capable of producing (meth)acrylate monomers of the general formula: 
where R H or CH3; and
where Rxe2x80x2=C1-C8 straight or branched alkylene. Such (meth)acrylate monomers include N-(2-methacryloyloxyethyl) ethylene urea (MEEU). Such monomers are useful as polymerized units in polymers and provide enhanced properties to such polymers, including adhesion.
One of the reactants that participates in the transesterification reaction is an hydroxyl alkyl imidazolidin-2-one of Formula III: 
where Rxe2x80x2=C1-C8 straight or branched alkylene; Suitable hydroxyl alkylene imidazolidin-2-one of Formula III include hydroxyethyl ethylene urea (HEEU).
The other reactants that participates in the transesterification reaction is an alkyl (meth)acrylate of Formula II: 
where R=H or CH3; and
where Rxe2x80x2=C1-C8 straight or branched alkyl;
Preferred alkyl (meth)acrylates include methyl methacrylate, butyl acrylate and ethyl acrylate. Methyl methacrylate is most preferred.
The mole ratio of hydroxyl alkyl imidazolidin-2-one of Formula III to alkyl (meth)acrylate of Formula II is typically from 1:1 to 1:20, preferably from 1:1 to 1:15, and more preferably from 1:1.2 to 1:10.
The reaction mixture also includes at least one polymerization inhibitor. Suitable polymerization inhibitors include diethylhydroxylamine, p-methoxy phenol, hydroquinone, phenothiazine, 4-hydroxy-2,2,6,6-tetramethyl piperidinyl free radical (4-hydroxy-TEMPO), 4-methacryloyloxy-2,6,6-tetramethyl piperidinyl free radical, and 4-hydroxy-2,6,6-tetramethyl N-hydroxy piperidine and mixtures thereof
The amount of inhibitor added to the reaction vessel is typically from 10 to 10,000 parts per million, based on the weight of the hydroxyl alkyl imidazolidin-2-one of Formula III, preferably from 100 to 5,000 ppm, and most preferably 200 to 3,000 ppm.
Suitable transesterification catalysts include dibutyl tin oxide, reaction products of dibutyl tin oxide with components in the transesterification of various alcohols with methyl meth(acrylate) or alkyl (meth)acrylates; dibutyl tin dimethoxide, reaction products of dibutyl tin dimethoxide with components in the transesterification of various alcohols with methyl (meth)acrylate or alkyl (meth)acrylates, methanolic magnesium methylate, lithium, lithium carbonate, anhydrous alkali metal alkoxides (such as lithium hydroxide), hydrates of alkali metal alkoxides (such as lithium hydroxide monohydrate) and mixtures thereof. Anhydrous lithium hydroxide and lithium hydroxide monohydrate are preferred.
The amount of the transesterfication catalyst added to the reaction mixture is typically from 0.1 to 10 mole %, preferably from 0.5 to 7 mole %, and more preferably from 1 to 5 mole %.
The process of the invention utilizes an Oldershaw distillation column. Suitable Oldershaw columns include a 10 plate X 1xe2x80x3 (2.54 cm) diameter column, a 5 plate X 1xe2x80x3 diameter column, a 10 plate X xc2xdxe2x80x3 (1.27 cm) diameter column, and a 32 tray column.
The process of the invention may also utilize a continuous or batch process provided such process permits unagitated contact between the transesterification catalyst and the hydroxyl alkyl imidazolidin-2-one of Formula III. For example, a process may employ an in-line mixer (such as static mixing in a tube reactor) or static impellar. Static mixing in a tube reactor is particularly useful for providing unagitated contact between the transesterification catalyst and molten hydroxyl alkyl imidazolidin-2-one of Formula III.
The transesterification step of the process of the invention may be carried out at a reaction temperature of 60xc2x0 C. to 140xc2x0 C., preferably 70xc2x0 C. to 125xc2x0 C. and most preferably, 85xc2x0 C. to 120xc2x0 C.
The transesterification step of the process of the invention may be carried out at pressures of 760 mm Hg to reduced or elevated pressures, preferably 400 mm Hg to 760 mm Hg.
All ranges used herein are inclusive and combinable.
The following abbreviations are used herein:
HEEU=hydroxyethyl ethylene urea
MMA=methyl methacrylate
Hg=Mercury
DI=deionized
GLC=gas liquid chromatography
xc2x0 C.=degrees centigrade
N2 =nitrogen
O2=oxygen
(meth)acrylate=methacrylate or acrylate
cc=cubic centimeter
cm=centimeter
hr=hour
mm=millimeter
ml=milliliter
mn=minute
ppm=parts per million
MEEU=N-(2-methacryloyloxyethyl) ethylene urea
MEMEU=N-(2-methacryloyloxyethyl)-Nxe2x80x2-(methacryloyl) ethylene urea
HPLC=quantitative high performance liquid chromatography
Some embodiments of the present invention will now be described in detail in the following Examples.